A short time later, they were contacted with reports of stabbings at the nearby Borough Market.
As calls continued to pour in, it became clear that the city was in the grip of a terrorist attack.
However, within eight minutes of the first call, the threats had been neutralised after police shot all three attackers dead.
Not only was this response time impressive in a logistical sense, it prevented what surely would have been a bigger tragedy on the streets of Central London.
Steve Hewitt, a Senior Lecturer in the Department of History, University of Birmingham in the UK, said that besides individual bravery, the success of the police operation was about learning from previous terrorist attacks, training and resources.
“The Metropolitan Police have been preparing for such a possibility for years now,” he wrote in The Conversation.
“Although, thankfully, this didn’t involve terrorists with firearms, those skills served them well in quickly dealing with the London Bridge attackers.”
In 2010, a major police training exercise, also involving members of the SAS, took place in London with the aim of dealing with a Mumbai-style attack. A spokeswoman from the Home Office noted at the time that:
“The police regularly train and exercise for a variety of scenarios with a variety of partners. It is right that we learn the lessons from previous incidents and that these inform and strengthen such procedures.”
Hewitt said the 2015 Paris attacks only reinforced the need for the police to be able to respond with speed and firepower.
“This approach was on display shortly after the Paris attacks, when the London police carried out a training exercise involving a scenario in which armed terrorists attack a shopping mall, a scenario that occurred in Kenya in 2013,” he said.
“The emphasis was on the swiftness of the response and the need for officers to quickly engage the terrorists, even if that meant ignoring wounded civilians and putting themselves at greater risk.”
Hewitt pointed to a senior police officer, who made it clear that speed was of the essence:
“We are asking them not to give first aid to the wounded. The most important thing is for them to get to the threat”.
But it’s also about having the resources to deploy against a threat, says Hewitt.
In January 2016, it was announced that 600 more armed officers would be deployed in London by the end of that year, boosting numbers to around 2,800 (or nearly 10% of the force).
“The number of armed police response vehicles was also doubled. More armed officers have been deployed in public places as well,” he said.
“These trends, in a country famously known for having unarmed police, will now only escalate in the aftermath of the Westminster attack in March and now London Bridge.”
Hewitt said the terrorism situation in the UK is “clearly in flux”.
“At the moment, the only pattern when it comes to terrorist attacks is that there is no pattern. Last night’s London attack appears to be in some ways a combination of the Westminster attack and the Lee Rigby murder,” he said.
“It differs greatly from the style of the May 22 Manchester attack. Nonetheless, members of the police will continue to prepare to deal with worst-case scenarios based on previous attacks that, undoubtedly, they hope will never materialise.”
Calls for better training after Malaysian Airlines bomb scare
Sydney shopping staff to get terror training
Why are teachers doing advanced gun training?
On 10:08pm on Saturday night, London’s Metropolitan Police Service received a call that a vehicle collided with pedestrians.